The effect of fungicide spray time on the incidence of stem canker of brassicas and seed yield of winter oilseed rape in Pomerania

The aim of this study was to determine the relationship between ascospore release and autumn fungicide spray time as well as, the incidence and severity of stem canker and seed yield. The concentration of ascospores in air was determined using Hirst-type volumetric samplers located in the region of Pomerania in central-north Poland, in the zone of intensive cultivation of oilseed rape, over three consecutive seasons from 2009/2010 to 2011/2012. A fungicide spray was most efficient, when applied 4 to 14 days after the highest concentration of Leptosphaeria ascospores was found in air samples. An application of fungicide at this time reduced the incidence of phoma leaf spotting by 12.5–24.7%, stem canker symptoms by 11.3–33.0% and decreased yield loss by 2.7–5.0 dt ha−1. The results demonstrate that knowledge about the concentration of pathogen inoculum in the air allows more efficient protection of oilseed rape against stem canker.